Geological assessments of the strata surrounding a borehole, can be obtained by a variety of techniques that involve lowering a device to a predetermined depth within the borehole and extending a boring tool from the device into the side wall of the borehole and into the strata surrounding it, to obtain a sample of the strata or to install one or more probes therein. Current industry practice uses devices such as samplers which are driven into the side wall of the borehole by explosive charges. However, these techniques permit penetration to only a small distance such as several inches from the borehole. The region immediately around the borehole is not necessarily representative of the surrounding strata, since the borehole walls are impregnated with drilling mud and are severely disturbed by the high bit loads of the borehole drill. There are advantages in obtaining access to strata formations a plurality of borehole diameters away from the borehole, such as a few meters away, where there is minimal contamination by the drilling mud and minimal terrain distortions produced by the borehole drilling.
A severe constraint on mechanical drilling in a lateral direction from the borehole, is imposed by the small dimensions of typical boreholes, which are generally not more than six inches in diameter. The boring apparatus must be contained within the confines of a housing which can fit into such a small borehole, and therefore requires a folding or collapsing device of relatively long reach for making long lateral penetrations. Apparatus that permitted such penetrations to be made for the installation of probes or the obtaining of core samples from the strata surrounding the borehole, would be of considerable value in the making of geological assessments, such as permitting more accurate determinations of oil extraction potential, geothermal energy extraction, and the like.